Q&A #19812

Teachers' Lounge Discussion: Explaining concept -x=2 is equal to x=-2

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From: Robert

To: Teacher2Teacher Public Discussion
Date: 2009090413:47:16
Subject: -x=2 is same as x=-2

To explain this can be a real challenge. It results from a basic
property of numbers named "Opposite of Opposites," where -(-a)=a and
may be visualized when a and negative a are plotted on a one
dimensional number line.It is clear that minus a negative a leaves
a.Consider the following metaphor.Let x= 2 buckets of cement that must
be be lugged up several flights of stairs by Moe accompanied by his
friend Joe.Moe soon tires and passes the hod to his friend. Moe is now
minus x= 2 buckets of cement.When Joe tires he passes the hod back to
Moe.Moe now has +x=2 buckets of cement, while Joe is minus 2 buckets.
Except for the transfer (transformation?) nothing has changed as the
hod still contains two buckets of cement. We ignore the translation of
position. I hope this helps. Robert.	

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